This invention relates to the field of isotope separation and more particularly to novel methods for separation of isotopes by adsorptive bubble separation mechanisms.
Nuclides, representing isotopes of various elements, find extensive practical scientific, industrial and chemical applications. Thus, for example, carbon, nitrogen and oxygen are used as medical tracers. Sulfur is used as a tracer in environmental studies. Nitrogen is used in nuclear magnetic resonance probes. A large number of other applications are known to those skilled in the art.
A variety of methods are used in the art for separation of isotopes. These include distillation, chromatography, centrifugation (or other kinetic techniques), gaseous diffusion, and photoexcitation. All of these methods operate on the basis of small differences between isotopes or compounds containing them with respect to mass, volatility or other physical or chemical properties. As a result of the relatively small separation factors afforded by these differentials, conventional methods for isotope separation are typically characterized by high energy requirements, very large numbers of stages, the need for elaborate and specialized equipment, low thoughput, and the need for sophisticated control. As a consequence, operations are generally quite expensive and even minor process upsets can result in substantial penalties in productivity, yields and/or quality.
Attempts have been made in the art to devise methods for isotopic separation based on differences in the behavior of isotopes in chemical exchange reactions. According to Biegeleisen, "Separation of Isotopes," Newnes, London, 1961, four requirements must be met for a chemical exchange isotope separation scheme to be successful. First, the element whose isotopes are to be separated must be distributed between two phases in different chemical forms and there must be efficient contacting of the two phases in a countercurrent stream. Secondly, rapid chemical exchange must take place between the chemical forms. Thirdly, there must be an appreciable isotope effect, i.e. a combination of reaction and phase equilibria which results in a difference between the phases of the system with respect to concentration ratio of the isotopes. Fourth, there must be a means for separating the two chemical forms after exchange. Ion exchange isotope separation processes are illustrated by Gupta, "Isotope Effects in Ion Exchange Equilibria in Aqueous and Mixed Solvent Systems," Separation Science and Technology, 14(9) pages 843-857 (1979) which describes ion exchange techniques for isotope separation and particularly discusses the role of solvent fractionation effects in ion exchange equilibria in mixed solvents. However, the need for repetitive adsorption and desorption and the limited availability of exchange sites detracts from the commercial utility of ion exchange as a method for isotope separation.
DeWitt et al. U.S. Pat. No. 3,965,250 discloses a method for separating isotopes of sulfur contained in a sulfur dioxide feed gas by continuous reaction of the gas with potassium hydroxide to produce an acid sulfite solution, and liberation of sulfur 34-rich sulfur dioxide by reaction of the acid sulfite with sulfuric acid, thereby producing a potassium acid sulfate by-product. The potassium acid sulfate is neutralized and the resultant potassium sulfate solution is subjected to electrodialysis for regeneration of potassium hydroxide and sulfuric acid used respectively for adsorption of SO.sub.2 and release of S-34 enriched sulfur dioxide gas. This process, which is relatively elaborate, requires a substantial energy input for operation of an electrodialysis unit, is relatively cumbersome and expensive to implement in an extensive cascade, and is limited to separation of isotopes of sulfur.
A need has remained in the art for relatively simplified methods of isotope separation which provide efficient enrichment without elaborate equipment or substantial energy expense.